Stress is recognized as a response which can lead to behavior disorders, and the symptoms associated with stress-induced behavior disorders are known as stress-related disorders; these are classified into several types of symptoms based on two factors: the nature of the stress and the disposition of the individual experiencing the stress. The symptoms span a wide range from simple habits such as finger sucking or onychophagy seen primarily during the infant period and resulting from light stress factors, to adjustment disorder and attention deficit hyperactivity disorder which are considered to be highly influenced by individual disposition, and further to acute stress disorder or posttraumatic stress disorder, which are associated with extremely intense stress beyond individual disposition (Shindan to Chiryo 91, 1333, 2003).
Recently, increased blood IL-1β has been reported in post-traumatic stress disorder patients (Biol. Psychiatry 42, 345, 1997), and research has focused on the relationship between IL-1β and neuronopathy.
Drugs used for stress-related disorders include benzodiazepine-based drugs used for insomnia and anxiety, serotonin reuptake inhibitors and tricyclic antidepressant drugs used to alleviate symptoms of flashbacks, adrenaline antagonists and anticonvulsant drugs used for symptoms of hypervigilance, and antipsychotic agents used for exaggerated startle response or increased irritability. However, all such agents are symptomatic treatment for improvement of superficial symptoms such as depression, insomnia and excitement, and unfortunately no agents for causal treatment exist at this time.
One possible treatment for stress-related disorders is to suppress their progression by removing the cause of stress. However, given the modern environment it is very difficult to eliminate the causative factors of stress.
Thus, to date no drug has existed which is effective as a pharmaceutical agent having a preventive or improvement effect on symptoms or diseases associated with stress-induced behavior disorders. Furthermore, applications to food products have been hampered by the limitation to components which produce no side effects.
The brain consists of a lipid mass-like tissue, with phospholipids constituting about ⅓ of the white matter and about ¼ of the gray matter. The polyunsaturated fatty acids in phospholipids of the various cell membranes in the brain consist primarily of arachidonic acid and docosahexaenoic acid. However, arachidonic acid and docosahexaenoic acid (DHA) cannot be synthesized de novo in animal bodies and must be directly or indirectly obtained through diet (for example, as the arachidonic acid and docosahexaenoic acid precursors, linoleic acid and α-linolenic acid).
Burgess et al. have demonstrated that arachidonic acid and DHA contents of plasma phospholipids are significantly lower in posttraumatic stress disorder patients (Am J Clin Nutr 71, 327S, 2000). It has also been reported that liver microsome Δ5-desaturase and Δ6-desaturase activity is reduced in separately bred stress model rats (Proc Soc Exp Biol Med. 205, 56, 1994), and the reduction in activity of these desaturases is believed to be responsible for a lack of brain levels of arachidonic acid and DHA, polyunsaturated fatty acids with a high degree of unsaturation.
On the other hand, several experiments have been reported using administration of arachidonic acid to animal stress models. Song et al. reported that administration of free arachidonic acid was not effective for IL-1β induced stress anxiety behavior models (J Lipid Res. 44, 1984, 2003). Also, Clements et al. describe giving attention deficit hyperactivity disorder (ADHD) models (spontaneously hypertensive rats, SHR) feed containing 0.5% arachidonic acid and 0.9% DHA for 8 weeks, and reported increased DHA in the brain phospholipids but no observable effect (Dev Psychobiol. 43, 57, 2003). No other reports indicate that administration of arachidonic acid improves stress-induced behavior disorders.
Thus, while it has been reported that arachidonic acid levels in the body are lowered by stress, it has not been clearly demonstrated whether arachidonic acid or compounds including arachidonic acid as a constituent fatty acid according to the invention are effective for the prevention or improvement of symptoms or diseases associated with stress-induced behavior disorders, and in fact the experiments conducted to date have been definitively negative.    Non-patent document 1: Shindan to Chiryo 91, 1333, 2003    Non-patent document 2: Biol. Psychiatry 42, 345, 1997    Non-patent document 3: Am J Clin Nutr 71, 327S, 2000    Non-patent document 4: Proc Soc Exp Biol Med. 205, 56, 1994    Non-patent document 5: J Lipid Res. 44, 1984, 2003    Non-patent document 6: Dev Psychobiol. 43, 57, 2003